-S.J.Singer and G.Nicolson proposed a membrane model called the fluid mosaic model.
WHY FLUID?
Most of the individual proteins and phospholipid molecules can drift laterally in the membrane.
WHY MOSAIC?
A membrane has various protein molecules embedded in the phospholipid bilayer.
PHOSPHOLIPID
-amphipathic molecule( has both hydrophilic region and hydrophobic region)
-polar head region is hydrophilic( attracted to water)
-non polar tail region is hydrophobic(repelled by water)
-phospholipid bilayer is semi-permeable.
TRANSPROT PROTEINS:
(A) CARRIER PROTEIN
-Protein molecule that has a shape that fits the shape of a specific molecule so that it can only carry specific molecules across the membrane.
(B) PORE PROTEIN
-Protein molecule that has a pore to provide a passage for a particular solute to pass through
video on movement of substance across a semi permeable membrane:
PASSIVE TRANSPORT ACROSS THE PLASMA MEMBRANE
-movement of substances across the plasma membrane from a region of high concentration to a region of lower concentration.
-does not require energy
SIMPLE DIFFUSION
-molecules diffuse across plasma membrane down the concentration gradient through the phospholipid bilayer until equilibrium is reached.
-soluble substances that can move across the plasma membrane by simple diffusion are:
- small uncharged polar molecules (oxygen,carbon dioxide,water)
- fat soluble substances (fatty acids,glycerol,vitamins ADEK)
OSMOSIS
-movement of water molecules down the concentration gradient until equilibrium is achieved.
FACILITATED DIFFUSION
-The substances cannot cross the plasma membrane by simple diffusion
-They need the help of transport proteins
-substances move by facilitated diffusion:
- mineral ions
- large,uncharged polar molecules(glucose,amino acids)
ACTIVE TRANSPORT ACROSS THE PLASMA MEMBRANE
-Movement of substances across the plasma membrane against the concentration gradient by expending metabolic energy
EFFECTS OF HYPERTONIC,HYPOTONIC AND ISOTONIC SOLUTIONS ON ANIMAL CELLS and PLANT CELLS
red blood cells(animal cells):
-HYPOTONIC SOLUTION
- water diffuses into the red blood cells by osmosis
- red blood cells gain water and swell and finally burst(because they have no cell walls)
- red blood cells undergo haemolysis
-HYPERTONIC SOLUTION
- water diffuses out of the red blood cells by osmosis
- red blood cells shrivel
- red blood cells undergo crenation
-ISOTONIC SOLUTION
- water molecules flow into and out of the membrane at the same rate(no net movement of water molecules)
- the shape of red blood cell is retained
plant cells:
-HYPOTONIC SOLUTION
-HYPOTONIC SOLUTION
- water diffuses into the cell by osmosis
- vacuole gains water,expands and exerts pressure outwards on the cell wall.
- this pressure is called as turgor pressure
- the turgidity gives the plant mechanical support
-HYPerTONIC SOLUTION
- water molecules diffuses out of the cell by osmosis
- the vacuole shrinks and becomes smaller
- the cytoplasm and plasma membrane are pulled away from the cell wall.
- The plant cells shrivels
- The cells become flaccid,causing the plant to wilt
- This process is called plasmolysis
- If the plasmolysed plant cell is immersed in a hypotonic solution,it undergoes deplasmolysis
-ISOTONIC SOLUTION
- water molecules flow into and out of the membrane at the same rate(no net movement of water molecules)
- the shape of red blood cell is retained
Nothing can stop the man with the right mental attitude from achieving his goal; nothing on earth can help the man with the wrong mental attitude.
Thomas Jefferson
Thomas Jefferson
Thanks
Regards@E-learning for SPM